CIRCULATING somewhere in the Pentagon is a proposal to increase vastly the number of circumstances in which employees may be asked to take lie detector tests. Pentagon officials told Post reporter George Wilson that this is just "an update" of a 1975 directive that allows such polygraph tests to be used in certain circumstances.

This is something like calling a declaration of war "an update" of a diplomatic note. The 1975 directive limits polygraph use to "serious criminal cases, national security investigations, and highly sensitive national security access cases"; it forbids the use of tests for selecting or screening employees; it says they can be used only to support other investigative techniques; it does not authorize the drawing of negative inferences from refusals to take the tests.

The proposed directive changes all these provisions: it allows tests to be used routinely for entering and existing employees, not only of the Defense Department but of civilian contractors; it allows them to be used in any unauthorized disclosure of classified information, however trivial; it says that adverse action can't be taken against employees solely because of polygraph evidence, but by inference polygraph evidence could be one basis for such action. Under the proposed directive, tests are still supposed to be voluntary, but already hundreds of Pentagon employees are being asked to waive their rights to refuse to take them.

This is not the first time Pentagon officials have tried to promote mass use of polygraph tests; similar proposals have been made several times over the past 30 years, in administrations of both parties. One reason, we suspect, is that CIA employees submit frequently to polygraph testing, with questions of an intimate nature intended, evidently, to disclose susceptibility to blackmail. So when Pentagon officials are especially worried about espionage -- or about embarrassing leaks to the press -- one reaction is to imitate the CIA and make lots of employees submit to lie detector tests.

It's an understandable response -- and a wrong one. The tests themselves are not reliable; that's why polygraph results are not admissible as evidence in court, and why they were described by former Sen. Sam Ervin as "an instrument of 20th century witchcraft." The questions likely to be asked range offensively far afield from the government's direct interest. The results inevitably will besmirch some blameless subjects and may exonerate some who ought to be suspect. There may be a case for such tests of employees of a secret agency like the CIA. But a blanket authorization of polygraph testing of 3 million employees of the Pentagon and defense contractors, the great majority of whom are exposed to low-level classified material or none at all, makes no sense.

The proposed directive is a response all out of proportion to the danger the government faces. It is a procedure aimed so imprecisely as to be unlikely to do what the government wants and so broadly as to be sure to do unintended harm. The burden is on the Pentagon to demonstrate why the nation suddenly faces such danger, or why Pentagon employees suddenly have become so unreliable, that this drastic change from current policy is necessary.